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초록

Alloying anodes for potassium-ion batteries offer large theoretical capacities but are constrained by mechanical degradation arising from nonuniform strain during electrochemical reactions. Here, we demonstrate that particle size dictates not only electrochemical reversibility but also the underlying alloying kinetics and associated chemo-mechanical response in Bi anodes. By systematically tuning particle dimensions, we identify a particle-size regime in which the alloying mechanism transitions from an interface-controlled, two-phase reaction to a diffusion-controlled alloying reaction. Operando Raman spectroscopy and operando Bragg coherent diffraction imaging resolve near-surface and internal strain evolution during potassiation, revealing that bulk Bi particles undergo anisotropic ion insertion, strain localization, and crystallographic-orientation-dependent mechanical instability. In contrast, nanoscale Bi suppresses phase coexistence, delocalizes strain, and accommodates volumetric changes more homogeneously, leading to reduced activation barriers and improved reaction kinetics. These results establish a mechanistic correlation between particle size, alloying kinetics, and strain evolution, providing a chemo-mechanical framework for designing mechanically durable alloying anodes.

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